igb: Create separate functions for generating cmd_type and olinfo

This change is meant to improve the readability of the driver by separating
out the cmd_type configuration and the olinfo configuration into their own
functions.  By doing this it is much easier to determine which ingredients
go into setting up these to portions of the descriptor.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>